The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A fuel cell converts chemical energy into electric energy by electrochemical reaction of hydrogen and oxygen, has a higher efficiency than an existing internal combustion engine, and produces water as a by-product of electrochemical reaction.
In the fuel cell, hydrogen as a fuel and oxygen (air) as an oxidant are respectively supplied to an anode (also called “fuel electrode” or “hydrogen electrode”) and a cathode (also called “air electrode” or “oxygen electrode”) of a membrane electrode assembly through the channel of a bipolar plate.
The hydrogen supplied to the anode is dissociated into hydrogen ions (protons, H+) and electrons (e−) by catalysts of electrode layers disposed at both sides of an electrolyte membrane. In this case, the hydrogen ions are transmitted to the cathode through the electrolyte membrane which is a cation exchange membrane, and the electrons are simultaneously transmitted to the cathode through a gas diffusion layer as a conductor and the bipolar plate.
At the cathode, the hydrogen ions supplied through the electrolyte membrane and the electrons transmitted through the bipolar plate react with the oxygen of air supplied to the cathode by an air supply device, thereby producing water. In this case, migration of the hydrogen ions causes electrons to flow through external conducting wires, which generates a current.
The humidity of air is very important for reaction in a fuel cell stack, and thus moisture is supplied to an air inlet by a humidifier for maintaining humidity. Air supplied with the moisture flows along the channel in the stack and reacts with hydrogen to produce water.
However, it is desired to remove the water produced by the reaction from the stack since it disturbs the flow of oxygen and hydrogen. Therefore, the water drained from the stack is collected in and discharged from a water trap.
That is, some of the moisture produced at the air electrode after the reaction flows to the hydrogen electrode, which disturbs the reaction in the fuel cell. Thus, there is a need for a water trap to discharge the produced condensate.
A drain valve is desired to discharge condensate from the water trap and a level sensor is desired to determine how much condensate is produced in the water trap.
If the level of the level sensor is not changed in response to the command to open the drain valve, it may be determined that the drain valve fails. However, we have discovered that it is difficult to determine whether or not the drain valve fails because, when the level sensor fails, the level thereof is not changed.